1. Field of the Invention
The present invention relates to an image display apparatus.
2. Description of the Related Art
Recently, flat panel displays which use electron-emitting devices have been studied actively. The flat panel displays have a rear plate equipped with electron-emitting devices, a face plate equipped with light-emitting members such as phosphors, and a panel obtained by joining the rear plate and face plate via a frame. Since an atmosphere of reduced pressure is maintained in the panel, the panel contains a spacer which serves as a support structure which can withstand atmospheric pressure to prevent the panel from being broken by the atmospheric pressure. It is known that the spacer, which is exposed to electron and other radiation reflected by the face plate, has its surfaces electrostatically charged, affecting trajectories of electron beams from the electron-emitting devices. To solve this problem, the spacer has been designed with various features. Specifically, antistatic coatings are applied to a spacer surface or surface geometry of the spacer is made concavo-convex. Together with the antistatic techniques, inventive approaches are discussed to make electrostatic charge on the spacer unnoticeable by controlling the trajectories of electron beams from electron-emitting devices in the vicinity of the spacer.
Patent document 1 describes a spacer manufacturing method by means of hot drawing and discloses a method for efficiently producing a spacer with a concavo-convex pattern formed on a surface.
Patent document 2 discloses that the resistance value of a high resistance film on a spacer surface has dependency on the direction of film formation.
Patent document 3 discloses that the shorter the distance between a spacer and an electron source, the greater the impact on electron-beam trajectories. This means that the narrower the pixel pitch, the larger the deviation in beam incident position to be corrected.
Patent document 4 discloses that beam position near a spacer is defined by height of scanning wirings.
Patent document 5 discloses that a concavo-convex pattern is formed on a spacer surface for electrostatic control and that groove shape is determined in such a way as to reduce incident angle dependency of a secondary electron emission coefficient δ of the spacer surface.
Patent documents 6 and 7 disclose that a concavo-convex pattern is formed on a spacer surface, that the concavo-convex pattern has a pitch distribution, and that a resistance distribution is produced on the spacer surface by the pitch distribution.
Patent document 8 discloses a technique for controlling trajectories of electron beams from surface conduction electron-emitting devices, each of which has a pair of device electrodes, near a spacer by inclining opposing faces of the device electrodes in a direction perpendicular to the longitudinal direction of the spacer.
<Patent document 1> Japanese Patent Application Laid-open No. 2000-311608 (U.S. Pat. No. 6,494,757)
<Patent document 2> Japanese Patent Application Laid-open No. 2003-282000
<Patent document 3> Japanese Patent Application Laid-open No. 2003-331761 (U.S. Pat. No. 6,992,447)
<Patent document 4> Japanese Patent Application Laid-open No. H08-315723 (U.S. Pat. No. 5,905,335)
<Patent document 5> Japanese Patent Application Laid-open No. 2000-311632 (U.S. Pat. No. 6,809,469)
<Patent document 6> Japanese Patent Application Laid-open No. 2003-223858 (U.S. Pat. No. 6,963,159)
<Patent document 7> Japanese Patent Application Laid-open No. 2003-223857
<Patent document 8> Japanese Patent Application Laid-open No. 2006-019253 (U.S. Patent Publication 2005/264166)
An image display apparatus illustrated in FIG. 2 includes a rear plate 81 which has matrix wirings and electron-emitting devices, a face plate 82 which has irradiated sections facing the respective electron-emitting devices, and a support frame 86, together forming an envelope 90. The image display apparatus, in which a high vacuum is maintained, has a spacer 100 to protect inner space from atmospheric pressure.
FIG. 3A illustrates a cross section as viewed from Y-side wires 89 near the spacer. The spacer is installed, being sandwiched between the Y-side wires on the side of the rear plate and an abutting member 131 on the side of the face plate. Because of an electric field formed by the spacer, electron-beam trajectories near the spacer differ from electron-beam trajectories distant from the spacer. Due to the difference in the electron-beam trajectory, the electron beams near the spacer and electron beams distant from the spacer differ in incident position of electron beams on the face plate. Consequently, density of light-emitting points changes near the spacer, causing bright lines or dark lines to be recognized in images and thus resulting in degradation of image quality.
FIG. 4 illustrates how electron beams near the spacer deviate in incident position of electron beams due to the electric field of the spacer. Effect of the electric field on electron-beam trajectories increases with decreasing distance from the spacer, and decreases with increasing distance from the spacer.
Recent studies by the inventors have suggested that electron beam deviations near the spacer are roughly classified into three types. The first is “initial beam deviation,” the second is “temperature-difference-dependent beam deviation,” and the third is “charging-dependent beam deviation.” The “initial beam deviation” is deviation in incident position of electron beams caused by potential distribution on a spacer surface and attributable only to potential difference between the face plate and rear plate. The “temperature-difference-dependent beam deviation” is deviation in incident position of electron beams caused by changes in the resistance value of a high-resistance potential regulation film on the space surface due to temperature difference between the face plate and rear plate. The “charging-dependent beam deviation” is deviation in incident position of electron beams caused by charging of the spacer surface which occurs when electron beams reflected by a metal back reach the spacer surface. Charging can be either positive or negative depending on a secondary electron emission coefficient of the spacer surface. Thus, the electron beam deviation near the spacer results from superimposition of the three types.
To correct the beam deviation, patent document 3 describes a method for correcting deviation in the incident position of electron beams by increasing the pixel pitch near the spacer according to the deviation in the incident position. Also, patent document 4 describes a method for correcting deviation in the incident position of electron beams by adjusting height of a member which abuts the spacer. Although these methods can correct the “initial beam deviation” to some extent, the methods cannot correct the “temperature-difference-dependent beam deviation” and “charging-dependent beam deviation” sufficiently.
In correcting beam deviation near the spacer, a method which forms concavo-convexity on the spacer surface covers a wide range of correction and can solve the initial beam deviation and charging-dependent beam deviation out of the three types of beam deviation. With the hot drawing process described in patent document 1, a spacer with a striped concavo-convex pattern formed on a longitudinal surface can be produced easily. This technique can also be used for examples of the present invention. To minimize charging of the spacer using a concavo-convex pattern on the spacer surface, it is necessary to consider the secondary electron emission coefficient δ, which is the value obtained by dividing the number of emitted electrons by the number of incident electrons in a unit area on the spacer surface. When δ is 1, the number of emitted electrons equals the number of incident electrons, and thus the spacer is not electrically charged. When δ is larger than 1, the proportion of the emitted electrons increases, causing the spacer surface to be charged positively. When δ is smaller than 1, the proportion of the emitted electrons decreases, causing the spacer surface to be charged negatively. The value of δ depends on material of an antistatic film on the spacer surface, surface geometry of the spacer, and an incident angle of the incoming electrons. If it is assumed that the incident angle is 0 when the electrons are incident perpendicularly on the spacer surface, the secondary electron emission coefficient increases with increases in the incident angle. Electrons are rarely incident perpendicularly on the spacer and are incident from the side of the face plate or rear plate in many cases. Thus, when the spacer surface is flat, δ becomes far larger than 1, tending to cause the spacer surface to be charged positively. Conversely, when the spacer surface contains concavo-convexity forming deep grooves, the incident angle can be kept low in the grooves and thus δ can be reduced. Based on these principles, patent document 5 describes a method for reducing charging by minimizing δ through formation of a concavo-convex pattern on the spacer. This method can reduce the “charging-dependent beam deviation,” but the concavo-convex pattern on the spacer surface also affects resistance distribution on the spacer surface and thus the “initial beam deviation,” making it difficult to control both types of deviation as desired.
The principle by which the “initial beam deviation” is corrected using a concavo-convexity distribution consists in producing a resistance distribution on the spacer surface using the concavo-convexity distribution and thereby producing a desired potential distribution. That is, since creepage distance varies with concavo-convexity, resistance on the spacer surface can be distributed according to the concavo-convex pattern. This technique is described in patent documents 6 and 7.
Incidentally, as a technique for correcting beam position, patent document 8 discloses a technique for ingeniously adjusting orientation of a pair of device electrodes. Specifically, the technique controls trajectories of electron beams from surface conduction electron-emitting devices, each of which has a pair of device electrodes, near a spacer by inclining opposing faces of the device electrodes in a direction perpendicular to the longitudinal direction of the spacer. Hereinafter, the device electrodes whose opposing faces are inclined in a direction perpendicular to the longitudinal direction of the spacer will be referred to as “inclined device electrodes.” However, an image display apparatus with a narrow pixel pitch results in reduction in drift distances and reduction in an angle of inclined device electrodes, which are important elements of inclined device electrodes, reducing amounts of their correction.
In view of the conventional problem described above, an object of the present invention is to implement a higher-quality image display apparatus by correcting differences in beam incident position resulting from differences in spacing distance from a spacer.